1. Field of the Invention
The present invention relates to a circuit substrate used for electronic apparatuses (e.g., audiovisual apparatuses, electrical appliances, communication apparatuses, computer apparatuses, and the peripheral devices thereof).
2. Description of the Related Art
Hitherto, a mounting structure in which mounting electronic components are mounted on a circuit substrate has been used.
Japanese Unexamined Patent Application Publication No. 2008-120922 describes a circuit substrate including a base that includes a plurality of resin layers stacked one above another, and conductive layers formed on upper and lower surfaces of the base.
To increase rigidity of the circuit substrate, a filler is contained in the resin layers of the base in some cases. In such cases, because of a difference in coefficient of thermal expansion between a resin material and the filler which are contained in the resin layers, the resin material and the filler may separate from each other, and a crack may grow along a gap separating them in a vertical direction. On the other hand, during use of the circuit substrate, there is a possibility that when a voltage is applied between the conductive layers spaced from each other with the resin layer interposed therebetween, a conductive material contained in the conductive layers is ionized attributable to moisture contained in the resin layers and part of the ionized conductive materials grows into cracks in the resin layers. As a result, the conductive layers are more likely to short-circuit each other, and electrical reliability of the circuit substrate is more likely to be reduced.